1. Field of the Invention:
This invention relates to methods and apparatus for emphasizing the sharpness of a picture to be reproduced and/or recorded upon the scanning and recording of the picture by means of a scanner used in plate-making for printing, facsimile transmission, or the like.
2. Description of the Prior Art:
Emphasis of the sharpness of a reproduced picture during picture processing of a scanned image input has heretofore been effected on the picture signals to be processed or on peripheral information related to the picture signals to be processed. When performing sharpness emphasis solely on the basis of processing picture signals, there is a drawback in that the emphasizing effect can be obtained only in the main scanning direction. Thus it is impractical to use such a sharpness emphasizing method in scanners for apparatus making printing plates and the like.
In the case of conventional methods and apparatus relying upon peripheral information of picture signals to be processed, a light beam 1, which has optically scanned a picture is, as illustrated in FIG. 1, branched by half mirror 2 and the picture is focused on masks 4a, 4b on their corresponding branched axes 3a, 3b. Then, light beams which have passed through apertures 5a, 5b formed through their corresponding masks 4a, 4b and having different aperture diameters d.sub.1, d.sub.2 are photoelectrically converted by photoelectric conversion elements 6a, 6b and thereafter converted to density signals by means of logarithmic compression amplifiers 7a, 7b, which are equipped with preamplifiers, thereby producing picture signals A, B, respectively.
The light which has passed through the aperture 5a is color-separated into the three colors red (R), green (G), and blue (B), and the resulting color-separated light beams result in, respectively, picture signals A.sub.R, A.sub.G, and A.sub.B, which are referred to as individual sharp signals.
The picture signal A, obtained by way of the smaller aperture diameter d.sub.1, is generally called a sharp signal, which is to be subjected to sharpness emphasis. On the other hand, the picture signal B obtained via the larger aperture diameter d.sub.2 is generally called an unsharp signal, which is a picture signal containing peripheral information related to the sharp signal A.
In order to emphasize the sharpness of the recording picture signal by means of the sharp signal A and unsharp signal B, the unsharp signal B is subtracted from the sharp signal A (the green component A.sub.G normally being used for this purpose) by a differential amplifier 8 and unsharp mask signal C output from the differential amplifier 8 is added to the sharp signal A (either A.sub.R, A.sub.G, or A.sub.B) by means of an addition amplifier 9, thereby obtaining as an output of the addition amplifier 9 a light exposed signal D (D.sub.R, D.sub.G, D.sub.B) which has already been emphasized (see FIG. 2).
The above-described sharpness-emphasizing method for picture signals, and its associated apparatus, is widely employed these days but is accompanied by a shortcoming in that it requires an optical system and signal-processing system to convert each density so as to obtain unsharp signals B, in addition to the optical system and signal-processing systems for sharp signals A.
The above sharpness-emphasizing method and apparatus has merit in that the emphasizing characteristic can be made directional by modifying the shape of the aperture 5b used to obtain the unsharp signal B; and, the emphasizing range can be changed by altering the aperture diameter d.sub.2. On the other hand, it also has a drawback in that a variety of masks have to be provided corresponding, respectively, to the desired manners of emphasis. Furthermore, the aperture diameter d.sub.1 of the aperture 5a for the sharp signal A is determined by the desired resolution of the sharp signal A. Therefore, it is necessary to change the aperture diameter d.sub.2 of the aperture 5b whenever the aperture diameter d.sub.1 is changed in accordance with the conditions such as magnification of reproduction, etc. Accordingly, it is generally required that the masks 4a, 4b be provided as combined sets associated with various resolutions of the sharp signal A.
One method and associated apparatus which is adapted to emphasize the sharpness of picture signals and has solved the above-described drawbacks of the prior art is disclosed in Japanese patent Laid-open No. #56-8140 of Mitsuhiko Yamada, filed by the present assignee. That method and apparatus is accompanied by a drawback, however, in that certain components or devices required to practice the method (namely, the components or devices corresponding to those indicated by numerals 32-38 in FIG. 4, which will be described hereinafter) become very complex.
Wherefore, it is an object of this invention to provide a sharpness-emphasizing method capable of simplifying the components and/or devices used for its practice yet being similar to the method and apparatus disclosed in the above-recited Japanese patent Laid-open No. #56-8140 and, therefore, an improvement thereto.